1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor apparatus which comprises a semiconductor substrate and plural elements formed on the substrate. More particularly, it relates to a method of manufacturing a semiconductor apparatus comprising elements arranged on a substrate at as high a density as in an LSI, in which method regions separating the elements are formed sufficiently narrow, thereby enhancing the integration density of the apparatus.
2. Description of the Related Art
To manufacture a semiconductor apparatus having a high integration density, like an LSI, plural elements are formed on a semiconductor substrate, and regions are also formed on the substrate to separate the elements from one another. In a known method, such regions (hereinafter called "separating regions") are formed by oxidizing the selected portions of an insulation layer. This selective oxidation is called a LOCOS process.
In the LOCOS process, a pattern mask of silicon nitride is formed on those portions of a semiconductor substrate (a silicon wafer) where elements will be formed. (These portions of the substrate will be referred to as "element regions.") When the pattern mask has been formed, the substrate is heated and oxidized. As a result, an oxide film is formed on those portions of the substrate which are not covered by the pattern mask and are thus exposed.
The LOCOS process is easy to perform, and serves to manufacture a semiconductor apparatus with a high degree of accuracy. In view of this, the LOCOS process is advantageous. However, when this process is peformed, thus forming narrower separating regions, thereby to enhance the integration density of the semiconductor apparatus, the following problem will arise.
When the substrate is heated and oxidized, with a pattern mask formed on the element regions of the substrate, even those unexposed portions of the substrate which extend along the edges of the mask patterns are oxidized, too. These portions are called "bird's beaks," and are usually as wide as about 0.6 .mu.m.
What is used as an element region is that portion of the nitride film-covered area which excludes the bird's beaks. This means that each separating region includes the bird's beaks. It is therefore difficult to make the separating region sufficiently narrow. The bird's beaks must be eliminated in order to enhance the integration density of the semiconductor apparatus.